8.2

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-24899

CVE-2026-24899: Fleet Windows MDM Azure AD JWT Authentication Bypass

Fleet is open source device management software. Prior to version 4.82.0, a vulnerability in Fleet's Windows MDM enrollment flow allows authentication tokens from any Azure AD tenant to be accepted. Because Fleet validates JWT signatures using Microsoft's multi-tenant JWKS endpoint but does not enforce the aud (audience) or iss (issuer) claims, any Microsoft-signed Azure AD access token containing the expected scopes can be used to authenticate to Fleet's MDM endpoints. If Windows MDM is enabled, an attacker with access to any Azure AD tenant can obtain a valid Microsoft-signed token and use it to enroll unauthorized devices and interact with Fleet's MDM management APIs. During device management, Fleet may expose sensitive enrollment secrets embedded in MDM command payloads, enabling further unauthorized access. Version 4.82.0 contains a patch. If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2026-24899

CVE-2026-24899:

8.2

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

SSVC / BOD 26-04 ↗

Exploitation NoneAutomatable YesTech Impact Total

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Package Name	Ecosystem	Vulnerable Versions	First Patched Version
github.com/fleetdm/fleet/v4	go	< 4.82.0	4.82.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in Fleet's Windows MDM enrollment flow, which allowed authentication tokens from any Azure AD tenant to be accepted. This was because Fleet did not enforce the aud (audience) or iss (issuer) claims in the JWT. An attacker could obtain a valid Microsoft-signed token from any Azure AD tenant and use it to enroll unauthorized devices and access Fleet's MDM management APIs.

The analysis of the patch reveals that the fix was implemented in two key functions:

server/service/microsoft_mdm.go:(*Service).authBinarySecurityToken: This function handles the authentication of the binary security token. The patch introduces validation for the aud (audience) claim, ensuring it matches the Fleet server's URL, and the tid (tenant ID) claim, ensuring it belongs to the list of configured Entra Tenant IDs. The vulnerable version of the code was missing these critical checks.
server/mdm/microsoft/wstep.go:GetAzureAuthTokenClaims: This function extracts claims from the Azure JWT. The patch adds logic to validate that the iss (issuer) claim matches the tid (tenant ID) claim. This prevents the use of tokens issued by a different, unauthorized tenant.

By adding these validation steps, the patch ensures that only tokens from the configured Azure AD tenant and intended for the specific Fleet instance can be used for MDM enrollment, effectively mitigating the authentication bypass vulnerability.

Vulnerable functions

Service.authBinarySecurityToken

server/service/microsoft_mdm.go

This function is responsible for authorizing the binary security token provided during Windows MDM enrollment. The vulnerability lies in the fact that before the patch, this function did not validate the `aud` (audience) and `tid` (tenant ID) claims of the JWT. This allowed an attacker with a valid token from any Azure AD tenant to authenticate and enroll a device. The patch adds checks to ensure the token's audience matches the Fleet server's URL and the tenant ID is in the list of configured Entra tenant IDs.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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